Ab initio excitation spectrum of the weak He⋯BF interaction

The adiabatic interaction energy (IE) of the ground He ( 1 S ) ⋯ BF ( X 1 Σ + ) and excited He ( 1 S ) ⋯ BF ( a 3 Π ) electronic states of the van der Waals (vdW) system He ⋯ BF are studied in the present contribution in the framework of the supermolecule approach at the RHF-CCSD(T) level of theory. Calculations predict a global minimum and a shallow local minimum separated by a saddle point for the ground state; the most stable configuration occurs at βe=180°, equilibrium distance Re=6.63 a_o and equilibrium dissociation energy De=21.87 cm⁻¹. The calculated IE for the excited 3 A ′ state reveals two local minima and a global minimum separated by saddle points; the most stable configuration occurs at βe=121°, R_e=6.15 a_o and De=28.27 cm⁻¹. The resulting IE of the excited 3 A ″ state reveals two minima separated by a saddle point; the most stable configuration occurs at βe=76°, R_e=6.02 a_o and De=38.47 cm⁻¹. The corresponding vertical electronic excitation energies and shifts in the fluorescent spectrum with respect to the isolated BF molecule are calculated as a guideline for future theoretical and experimental work.